As an antenna device in the related art, a slot antenna illustrated in FIGS. 14(A) to 14(C) is known (for example, refer to Patent Literature 1). FIGS. 14(A) to 14(C) are perspective views illustrating a dielectric substrate, a conductive layer, and a reflection plate in the slot antenna in the related art.
The slot antenna has a microstrip line 202 on a front surface of a dielectric substrate 201, and a conductive layer 203 is arranged on a rear surface of the dielectric substrate 201. In addition, a plurality of slots 204a to 204d is formed in the conductive layer 203. The plurality of slots 204a to 204d receives electric power via the microstrip line 202, thereby realizing emission in a horizontal direction (−X direction) of the dielectric substrate 201. In addition, a cavity-formed reflection plate 205 in which a raising-processed portion 206 is disposed is arranged in the plurality of slots 204a to 204d, thereby achieving antenna performance excellent in a front back ratio (FB ratio).